The present invention relates to a device for guiding an endless band-saw blade around two deflection stations arranged at a distance to one another, with which the band-saw blade in each case is guided with a constant radius and at least one straight-lined path arranged therebetween.
The invention relates also to a device for measuring and setting the tension of a band-saw blade, with which this is guided according to the method. Furthermore the invention includes a band-saw machine with which the band-saw blade is guided.
As is known band-saw blades with their use are to remove material where possible. This means that the band-saw blades in their straight path course between the two deflection stations are to be absolutely flat. Furthermore a band-saw blade is to be guided in the deflection stations at an equal as possible location. If the band-saw blade in the guiding region of the deflection stations is only arcuate in the direction of the course of the deflection stations, i.e. running practically on a semi-circle, then the drums, rollers or deflection wheels must be practically cylindrical. On a cylindrical surface the band-saw blade would however have an insufficient guiding and would run off course. Accordingly one has provided these deflection rollers, drums or wheels with slightly cambered surfaces. The band saw blades must as a result on the staright paths run completely level whilst in the curvature of the deflection station should have a cambered shape. This is to be achieved in that by way of pressure rollers a tension is pressed into the so-called body of the band-saw blade which leads to the fact that the blade in the arcuate region assumes a curved shape.
This rolling-in of tension in the band-saw blade is an extremely akward activity which entails much experience. The correct setting of this pre-tension has an essential influence on the problem-free operation in a sawing mill, on the output which may be achieved, and above all on the life expectancy of the band-saw blade. By way of the pressure rollers however not only is the tension in the band-saw blade set but also simultaneously its shape is determined. Thus possibly present unevenesses may be corrected by way of the pressure rollers and likewise the exact straight running of the rear edge of the band-saw blade.
Until today it is common for the man skilled in the art who carries out this work to lift the free, non-tensioned band-saw blade and to fix and mark in the meniscus region by way of a ruler or by way of a template the cambering of the band-saw blade, at which location possible corrections are carried out. This is essentially work carried out by hand whilst subsequently by way of a simple machine with pressure rollers the tensions are pressed into the band-saw blade.
From the European patent application EP-A-0 820 829 (Walter Oppliger, Uetendorf) there is known a device with which the band-saw blade may not only be pre-tensioned by way of suitable pressure rollers but with which additionally the pre-tension in an arcuate course of the band-saw blade may be measured. With this device one imitates the principle of the procedure made by hand. With this the band-saw blade with respect to a rest is guided upwards and from this higher region in a free curve is again led back onto the rest. The meaurement here is effected in the descending region, by which means the desired curvature is not exactly measured but the inverse cambering. Attempts by the applicant have now shown that this measurement yields unreliable results. The reason for this is the free running of the band-saw blade which is not controlled, wherein the still present residual tensions in the blade changes the course of the curve and as a result also co-influences the cambering itself.
On the market there is further obtainable a device for measuring and forming the tension in a band-saw blade similar to the mentioned device according to EP-A-0 820 829. Here the measurement is done shortly before the transition into the straight-lined path, still in the region of the constant radius. An imitation of this measuring path by the applicant likewise showed inaccurate and varying results. In order to achieve results which are as constant as possible the band-saw blade in this machine marketed by the company Ishida Trading Co. Ltd. the band-saw blade must have a sufficient tensile stress. In order to obtain as constant as possible results the band-saw blade in the measuring region must be guided as uniformly as possible by way of holding-down devices. This however results in a constraint which is in conflict with the desired impressed tensions and leads to falsifying results.
By way of very costly trials the applicant has finally found a solution which leads to extremely exactly repeatable measuring results. Assuming that one knows that the band-saw blade in the straight-lined path course is to be absolutely level and in the arcuate region is to have a cambering inasmuch as this is concerned one may assume that the band-saw blade in the transition region practically thus on a line assumes a discontinuous change in shape. This discontinuous change however leads to the undesired irregularities with the measurements. It was therefore the object of the present invention to provide a method with which the discontinuous change in tension in the band-saw blade may be avoided.
As a particularly suitable shape of a path region with an increasing radius has shown to be the shape of a clothoid arc.
The guiding of the band-saw blade according to the method resulted in the possibility of realising a device for measuring and setting the tension of a band-saw blade which permits exact measurements in a manner such that one may construct a device by way of which the band-saw blades may now be correctly shaped.
From the consideration that evidently the guiding according to the invention of a band-saw blade avoids the discontinuous change of the geometry of the band-saw blade one has come to the conclusion that the tension change which has been discontinuous up to now may also be responsible for the fracture formation in the band-saw blade.